Abstract

Haploinsufficiency, having only one functional copy of a gene, leads to a wide range of human disease and has been associated with over 300 genes. Here, we tested whether CRISPR activation (CRISPRa) could rescue a haploinsufficient disease in vivo. Haploinsufficiency of Sim1, a transcription factor involved in the leptin pathway, results in severe obesity in humans and mice. CRISPRa targeting of either the Sim1 promoter or its ~270kb distant hypothalamic enhancer using transgenic mice, rescued the obesity phenotype in Sim1 heterozygous mice. Interestingly, despite using a ubiquitous promoter for CRISPRa, Sim1 was upregulated only in tissues where the promoter or enhancer are active, suggesting that cis-regulatory elements can determine CRISPRa tissue-specificity. To further relate this to therapy, we injected CRISPRa adeno associated virus into the hypothalamus, leading to reversal of the obesity phenotype. This therapeutic strategy could be used to rescue numerous diseases resulting from altered gene dosage.